A conventional gun reamer tool includes a cutting blade and one or more support members which are supported at intervals around the circumference of a rotary shaft (e.g., the reamer head). The shaft, along with the blade and the support members, rotate so that the physical interference between the rotating blade and the workpiece cause a hole to be either bored or reamed in the workpiece. During this machining operation, the rotating support members are positioned so that they support the inside surface of the hole being machined (e.g., either reamed or bored) by constraining radially directed motion of the blade relative to the workpiece.
In some conventional machining center rotating machine tools, lubricant is supplied to the vicinity of the cutting blade through the rotating shaft. An example is shown in U.S. Pat. No. 5,775,853 issued on Jul. 7, 1998, the disclosure of which is herein incorporated by reference.
This support and constraint supplied by the support members help to control the shape (e.g., cylindricity or circularity) of the hole, and help to maintain a constant alignment of the central axis of the hole along the length of the hole (in other words, the hole is straighter). For this reason, gun reamers are often used in applications where holes need to be precisely and accurately machined. Such precision applications may also be needed in the manufacture of automobile parts such as cylinder bores in engine blocks, connecting rod bores and piston wrist pin bores.
Gun reamers are also especially useful where the hole being cut is relatively long (such as the bore of a gun barrel), because the support members will remain in the proximity of the cutting blade, even when the blade has cut a long distance into the workpiece.
One potential shortcoming of conventional gun reamers is that they cannot be adjusted to cut holes of different sizes. Most conventional gun reamers are designed with support and blade members rigidly constrained to the reamer head so that the head can cut holes of just one predetermined radius. Another potential shortcoming of conventional gun reamers is that the blade and support members wear at different rates, which can cause seizure or variation in the diameter and/or circularity of the holes cut by the gun reamer.
In most machine tool operations, including boring and reaming, the friction between the tool and workpiece generates tremendous amounts of heat energy, which can reach temperatures of 2000.degree. F. (1100.degree. C.) and above. If left uncontrolled, such heat could severely damage (e.g., cracking or fracturing) the tool, thus reducing its tool life, making machine tool operations more dangerous and expensive, and reducing the quality and precision of the workmanship. In addition, heat generated friction can discolor the workpiece, and can damage or remove temper or heat treatments. It is commonly known in the industry that coolant can be introduced to the machining area, such as by spraying, to reduce friction between the tool and workpiece by providing coolant fluid between the cutting tool and the workpiece, and to help remove heat energy generated in machine tool operations.
Although coolant fluid can be supplied to the machining area, it is often difficult to insure that such fluid actually makes its way to the interstices between the tool and all of the workpiece surfaces being machined. Additionally, fluid can evaporate quickly due to the high temperatures involved in machining operations. Thus, larger volumes of coolant fluid must generally be continuously supplied to the machining area for the tool to operate effectively. This need to keep coolant fluid between the tool and wall of the bore hole becomes even more problematic in operations where coolant fluids cannot be introduced in close proximity to the machining areas while the tool is engaged with the interior surface of the workpiece.
During use, the work engaging surface of the tool (e.g., the cutting blade and/or support member) can also become loaded with particles or recently cut chips from the interior surface of the workpiece, which in turn, reduces the accuracy and effectiveness of the tool through deteriorating machining ability, and/or clogging of conventional coolant fluid supply openings. It is obviously preferred that the potential for this undesired loading of particles be reduced, and that any loaded particles be removed from the tool as quickly as possible. Typically, nozzle arrangements, such as an external cleaning jet, are provided independent of the tool, for injecting coolant fluid at increased velocities toward the work engaging surface and the work surfaces of the workpiece to wash away particles, to remove particles already loaded on the work surface, and to cool the tool and the workpiece. As mentioned before, it is often very difficult to insure that the fluid sprayed in this way actually reaches the most critical areas of the tool/workpiece interface.
Other attempts to deliver coolant fluid to the machining area have included air or other pneumatic carriers. As with externally applied liquid coolants, when pneumatic carriers are used, resulting turbulence can hinder the machining operations, and often fluid cannot infiltrate into the actual machining area. Previously, attempts to address these two requirements of cooling and cleaning the tool and workpiece have tended to reduce the accuracy and utility of the tool.
As can be seen, currently available tools have a number of shortcomings that can greatly reduce the accuracy of the tools, the tool's life, and its ability to use these tools with automatic tool changing systems. The current structures and assemblies provide a tool having working surfaces that cannot expand to accommodate varying and different uses and needs. Such assemblies can result in uneven machining, and reduces the assembly's usable life. A need currently exists in the machinery industry for a tool with a work engaging assembly having accurately controlled machining diameters so that holes of different sizes can be cut, so that tools cannot become oversized a result of excessive strokes of the tools, and so that the tool can expand in a radial direction uniformly and selectively.